Drilling fluid treatment

ABSTRACT

A method for treating well drilling fluid to remove substantially all suspended solid particles wherein the drilling fluid is centrifuged to remove particles of sizes down to about 20 microns in diameter followed by adding a flocculating agent to form flocs of particles from about 20 microns to less than 2 microns in diameter, and filtering the flocs from the drilling fluid to provide a liquid substantially free of suspended solid particles for reuse as a drilling fluid.

United States Patent [191 Bone, III

[ 1 June 5, 1973 154] DRILLING FLUID TREATMENT [75] Inventor: Lee Bone,III, Richardson, Tex.

[73] Assignee: Atlantic Rlchlleld Company, New

York, N.Y.

[22] Filed: May 3, 1971 [21] Appl.No.: 139,416

Donald 57 ABSTRACT A method for treating well drilling fluid 'to removesubstantially all suspended solid particles wherein the [52] US. Cl...210/73, 175/66, 210/54 i g i is i g d to remove particles of i [51]Int. C1. "E2"! 21/04 down to about 20 microns in diameter followed by[58] of Search ..210/73, 54', 175/66 a flocculating agent to form n ofparticles from about 20 microns to less than 2 microns in [56] RehrencesCited diameter, and filtering the flocs from the drilling fluid UNITEDSTATES PATENTS to provide a liquid substantially free of suspended aSO'lld particles for reuse as a drllllng fluid. 3,433,312 3/1969 Burdynet a1. ..175/66 2,870,990 1/1959 Bergey ..l75/66 5 Claims, 2 DrawingFigures 7 3 f 9 SCREEN 64 currmss MUD PIT PRIOR ART WEIGHTING SOLIDSPatented June 5, 1973 3,737,037

7 3 f 9 V SCREEN 5 4 J 1 I CUTTINGS MUD WEIGHTING souos A I7 /I7 PRIORART 9 SCREEN 4 CUTTINGS PIT WEIGHTING SOLIDS 26 souos souos 2 2 P-INVENTOR FIG. 2 LEE BONElIT I Wax $724M ATTORNEY DRILLING FLUIDTREATMENT BACKGROUND OF THE INVENTION Heretofore suspended solids havebeen removed from a drilling fluid utilizing mechanical decanting centrifuges such as the Sharples Super-D-Canter. Such a procedure isdisclosed in U.S. Pat. No. 2,870,990, the disclosure of which isincorporated herein by reference.

In the prior art procedures weighting materials such as barite, whichare purposely added to the drilling fluid to give it substantiallyincreased weight to counteract elevated downhole pressure, is firstremoved by the use of a mechanical decanting centrifuge. It is desirableto remove the weighting material separately from other less densesuspended solids so that the weighting material can be reused in otherdrilling fluid. The thus treated drilling fluid is then subjected to asecond mechanical decanting centrifuge to remove solid particles largerthan 2 microns in diameter. It is taught in the prior art that acentrifuge which will remove particles down to 2 microns in diametermust develop a centrifugal force of at least 2,100 times the force ofgravity and that centrifuges which develop less than 2,100 times theforce of gravity are not satisfactory because the effluent from such acentrifuge will contain a quantity of suspended solids which preventsreuse of the effluent as a drilling fluid.

Thus, the prior art teaches the necessity of removing suspended solidsdown to 2 microns in diameter which necessity requires the use of amechanical centrifuge.

A mechanical centrifuge which will remove suspended solids down to 2microns in diameter of necessity is very large, expensive, operates on alow throughput of drilling fluid, and has low efficiency as regardssolids separation.

For work in the field around a drilling rig it is desirable not to betied down to large expensive low efficiency mechanical centrifuges.

It is also taught in the prior art, Oil and Gas Journal, May 25, 1970,p. 65, that suspended solids in drilling fluid adversely affect thedrilling rate which adds to drilling time and cost, increases drillingfluid viscosity, increases pump pressure and wear, increases fuelconsumption, increases bit wear, and the like. Thus, it is desirable tocome as close as possible to removing all suspended solids, even thosewith a diameter of less than 2 microns.

SUMMARY OF THE INVENTION According to this invention, the necessity forlarge, expensive mechanical centrifuges which will remove solidparticles down to 2 microns in diameter is eliminated withouteliminating the function of such a centrifuge and even with animprovement in results in that particles smaller than 2 microns are alsoremoved. This is accomplished by centrifuging the drilling fluid toremove solid particles of sizes down to about microns in diameter andthereafter adding to the thus centrifuged drilling fluid at least oneflocculating agent in an amount effective to form flocs of substantiallyall remaining solid particles of sizes from about 20 microns to lessthan 2 microns in diameter, and filtering the flocs from the drillingfluid whereby substantially all of the liquid portion, including anydissolved chemicals, is retained for reuse and is in a physical statesuch that it is substantially free of suspended solids includingsuspended solids of a diameter smaller than 2 microns.

By removing solid particles no smaller than about 20 microns by way ofcentrifuging the need for a large expensive mechanical centrifuge suchas a decanting centrifuge is eliminated and" nonmechanical centrifugessuch as cyclone separators can be substituted which are not as large noras expensive as mechanical centrifuges which develop at least 2,100times the force of gravity. The nonmechanical centrifuges can process ahigher through'putof drilling fluid liquid with higher efficiency thansuch mechanical centrifuges. In addition, a large portion of the solidsseparation function is transferred from centrifuging to flocculationwhich is carried out chemically in a pit or tank and requires no bulkyequipment like mechanical centrifuges.

Accordingly, not only is the requirement for mechanical centrifugeseliminated and replaced with much smaller less expensive equipment suchas cyclone separators and flocculation tanks, but also the overall results of solids removal is substantially improved in that solidparticles smaller than 2 microns are also removed.

Accordingly, it is an object of this invention to provide a new andimproved method for treating well dril-' ling fluid. It is anotherobject to provide a new and improved method for separating suspendedsolids from a well drilling fluid to an extent such that the liquidportion of the well drilling fluid is suitable for reuse as such. It isanother object to provide a new and improved method for separatingsuspended solid particles from a well drilling fluid so that the onlywaste is solid particles as opposed to liquid-which are more easilydisposed of in the environment without polluting same.

Other aspects, objects, and advantages of this invention will beapparent to those skilled in the art from this disclosure and theappended claims.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a flow schemeaccording to the prior art.

FiG. 2 shows a flow scheme in accordance with this invention.

More specifically, FIG. 1 shows a wellhead l which is in communicationwith a wellbore 2 extending down into the earth. Other drillingequipment normally associated with wellhead l is not shown for sake ofbrevity but is well-known in the art as shown by U.S. Pat. No.2,870,990. Drilling fluid is pumped into the wellbore by way of pipe 3from one or more drilling fluid (oftentimes referred to as mud ordrilling mud) storage pits 4.

The drilling fluid entering wellhead 1 passes down into wellbore 2through drill pipe (not shown), exits through the drill bit at thebottom of the wellbore, and returns to the earth's surface 5 by way ofthe annulus between the exterior of the drill pipe and the interior ofthe wellbore. When the returning drilling fluid reaches wellhead 1 it isremoved therefrom by way of pipe 6. Pipe 6 carries the drilling fluid toa shale shaker or screening means 7 which separates the large cuttings(rock and other earth material cut loose by the bit and carried to thesurface by the drilling fluid) from the drilling fluid. The cuttings areremoved from the system as waste by way of pipe 8 and the drilling fluidwhich still contains suspended solids from about 1 inch in diameter downto submicron diameters is passed by way of pipe 9 to a mud pit 4.

In this invention a particle size is referred to as its diameter. Theterm diameter is meant to also apply to particles which are notgenerally spherical and in such a situation to refer to the largestcross-sectional dimension of the nonspherical particle.

Drilling fluid from one or more mud pits 4 is removed for treatment byway of pipe 12.

Depending upon the pressures encountered by gases, liquids, and the likeentering wellbore 2 from the earth, a drilling fluid may or may not needa weighting material added thereto to counteract the wellbore pressureand to keep this pressure from blowing the drilling fluid out the top ofthe wellhead. Thus, if low pressure is encountered in wellbore 2 thedrilling fluid may be an unweighted fluid which means that no weightingmaterial has been added thereto. However, if high pressure isencountered in wellbore 2 the drilling fluid most likely will be aweighted fluid. The weighting material employed is normally quite denseand therefore has a density substantially greater than any of the othersolids suspended in the drilling fluid including small cuttings.

When a drilling fluid is weighted, it is desirable to separate theexpensive weighting material out from the drilling fluid separately sothat it can be added to other drilling fluid and therefore reused in thesystem.

FIGS. 1 and 2 both show a treatment system for weighted drilling fluid.It should be noted that if the drilling fluid to be treated is notweighted the separate centrifugation step for removing weighting solidswill be eliminated for this invention applys to weighted or unweightedsystems.

In FIG. I pipe 12 carries the drilling fluid to a conventionalmechanical centrifuge 13 such as adecanting centrifuge whereby, bymechanical means, the drilling fluid is subjected to forcessubstantially greater than gravitational force so that the weightingsolids migrate out of the drilling fluid and are removed as asubstantially dry particular solid stream by way of pipe 14.

The thus treated drilling fluid then passes from mechanical centrifuge13 by way of pipe 15 to a second mechanical centrifuge such as theSharples Super-D- Canter which develops at least 2,100 times the forceof gravity to remove solid particles down to but not below 2 microns indiameter. The liquid effluent from mechanical centrifuge 16 is thenpassed by way of pipe 17 back to mud pit 4.

FIG. 2 shows substantially the same process steps as FIG. 1 for aweighted drilling fluid down to pipe 15. However, the mechanicalcentrifuge 16 of FIG. 1 is eliminated in the invention of FIG. 2.Instead there is employed a nonmechanical cyclone centrifuge 20 which ismerely a spiral conduit which imposes nowhere near 2,100 times the forceof gravity on the drilling fluid being treated but which will separateout solid particles down to 20 microns in diameter. These particles areremoved by way of pipe 21..

The drilling fluid still containing suspended solids smaller than 20microns in diameter is passed by way of pipe 22 to a tank 23 in whichone or more flocculating agents are mixed with the drilling fluid andthe mixture allowed to remain until flocs of substantial size are formedfrom the suspended solid particles of diameter smaller than 20 microns.

Thereafter, the drilling fluid containing flocs of solid particlespasses by way of pipe 24 to a filter 25 wherein the flocs are filteredfrom the liquid and removed by way of pipe 26.

4 The remaining liquid drilling fluid which is now substantially free ofsuspended solids including solids having a diameter smaller than 2microns is passed by way of pipe 27 back to mud pit 4 for reuse asdrilling fluid liquid.

One or more of a very large number of known flocculating agents can beemployed. Such known flocculatalkali metal carboxymethylcellulose;halides of alumi-.

num, iron, nickel, and cobalt; aluminum sulfate; alkali metal aluminate;alum; bentonite; attapulgite; sepiolite; hydrous mica; and kaolin. Sincethese flocculating agents are known and commercially available furtherdiscussion thereof is, for the sake of brevity, omitted.

The amount of flocculating agent or agents added to the drilling fluidwill vary widely depending upon the agents themselves and the particularcomposition of the drilling fluid but will generally be an amounteffective to form flocs of substantially all remaining solid particlesof sizes of from about 20 microns to less than 2 microns in diameter. Itis preferable that the amount of flocculating agent added be sufficientto form flocs that will be retained on a 200 mesh sieve (Tyler SieveSeries). Generally, from about 0.01 parts per million to about 5 weightpercent based on the total weight of the drilling fluid of one or moreflocculating agents can be added.

After the addition of the flocculating agent or agents stirring formixing can be employed if desired. The formation of the flocs is thenallowed to carry on under ambient conditions of temperature and pressurefor a desired time such as at least about 5 minutes.

Filtering of the flocs from the drilling fluid can be carried out in anydesired manner such as filtering with conventional screens or sieves,filtering through a sand bed, diatomaceous earth bed, and the like.

This invention is applicable to any known drilling' Example A process iscarried out using the apparatus substantially as shown in FIG. 2 whereinthe'drilling fluid is composed of diesel oil having added thereto, basedon the weight of the diesel oil, 5 weight percent barite, 3weightpercent attapulgite clay, and 1 weight percent fatty acidemulsifier.

The drilling fluid recovered from wellhead l by way of pipe 6 hascuttings which have a particle diameter greater than one-eighth inchremoved by screen 7. Drilling fluid removed from mud pit 4 by way ofpipe 12 contains as suspended solid particles-cuttings of a diametersmaller than one-eighth inch, barite particles varying from minus 20mesh (Tyler Sieve Series) to less than 2 microns and attapulgiteparticles in the same particle size range as the barite. The drillingfluid is passed through a decanting centrifuge 13 from whichsubstantially only barite particles are separated by way of pipe 14 andthe effluent from centrifuge 13 passes by way of pipe 15 to a cycloneseparator 20. Solid particles of attapulgite, cuttings, and some barite,are separated by way of pipe 21, these cuttings varying from slightlysmaller than one-eighth inch in diameter to 20 microns.

The liquid effluent from cyclone 20 passes to floc tank 23 to which isadded 1 weight percent, based on the weight of the liquid effluent, ofpartially hydrolyzed polyacrylamide as disclosed in U.S. Pat. No.3,463,730, the disclosure of which is incorporated herein by reference.The mixture of drilling fluid and partially hydrolyzed polyacrylamide isheld at ambient conditions of temperature and pressure for minutes afterwhich it is passed through a sand bed filter 25 in which flocs of solidparticles varying from microns to less than 2 microns in particle sizediameter are removed leaving substantially solids free liquid for returnto mud pit 4.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a method for treating well drilling fluid containing suspendedsolid particles in a wide range of particle sizes down to less than 2microns in diameter, the improvement comprising centrifuging saiddrilling fluid to remove any weighting agent present, thereaftercentrifuging said drilling fluid with a nonmechanical centrifuge toremove remaining solid particles of sizes down to about 20 micronsindiameter, adding at least one flocculating agent to the thus centrifugeddrilling fluid in an amount effective to form flocs of substantially allremaining solid particles of sizes from about 20 microns to less than 2microns in diameter, and filtering said flocs from said drilling fluidwhereby substantially all of the liquid portion including any dissolvedchemicals is retained for reuseand is substantially free of suspendedsolids.

2. A method according to claim 1 wherein said centrifuging to removeweighting material is accomplished with a mechanical decantingcentrifuge, and said centrifuging to remove less dense particles isaccomplished with a nonmechanical cyclone centrifuge.

3. A method according to claim 1 wherein said at least one flocculatingagent is selected from the group polyacrylates; polyacrylamides;polyamines; polyamides; partially hydrolyzed polyacrylamides;methylcellulose; carboxymethylcellulose; alkali metalcarboxymethylcellulose; halides of aluminum, iron, nickel, and cobalt;aluminum sulfate; alkali metal aluminate; alum; bentonite; attapulgite;sepiolite; hydrous mica; and kaolin.

4. A method according to claim 1 wherein said at least one flocculatingagent is added to said drilling fluid in an amount sufiicient to formflocs that will be retained on a 200 mesh sieve.

5. A method according to claim 1 wherein said at least one flocculatingagent is added to said drilling fluid in an amount of from about 0.01ppm to about 5 weight percent based on the total weight of the drillingfluid.

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2. A method according to claim 1 wherein said centrifuging to removeweighting material is accomplished with a mechanical decantingcentrifuge, and said centrifuging to remove less dense particles isaccomplished with a nonmechanical cyclone centrifuge.
 3. A methodaccording to claim 1 wherein said at least one flocculating agent isselected from the group polyacrylates; polyacrylamides; polyamines;polyamides; partially hydrolyzed polyacrylamides; methylcellulose;carboxymethylcellulose; alkali metal carboxymethylcellulose; halides ofaluminum, iron, nickel, and cobalt; aluminum sulfate; alkali metalaluminate; alum; bentonite; attapulgite; sepiolite; hydrous mica; andkaolin.
 4. A method according to claim 1 wherein said at least oneflocculating agent is added to said drilling fluid in an amountsufficient to form flocs that will be retained on a 200 mesh sieve.
 5. Amethod according to claim 1 wherein said at least one flocculating agentis added to said drilling fluid in an amount of from about 0.01 ppm toabout 5 weight percent based on the total weight of the drilling fluid.